1. Field
The present invention is related to transconductance devices.
2. Related Art
Transconductance devices are used as a basic building block in circuits to convert differential input voltage signals to differential output current signals. FIG. 1 shows a transconductance device 100 and FIG. 2 shows an ideal transconductance characteristic curve 200 over a range of differential input voltage signals Vsig. The transconductance Gm (e.g., differential output current (Io) over differential input voltage (Vsig)) is linear, if the derivative of the differential output current with respect to the differential input voltage signal Vsig is constant across all values of the differential input voltage Vsig.
In FIG. 1, the input and output node voltages are defined as follows:V+=Vcm+Vsig/2V−=Vcm−Vsig/2where Vcm is the DC common mode voltage and Vsig is the amplitude of the differential input voltage signal. The input and output node currents are defined as follows:I+=Icm+Isig/2I−=Icm−Isig/2
where Icm is the DC common mode current and Isig is the amplitude of the differential output current signal.
The input differential signal which is the voltage differential of V+ and V− can be expressed as:V+−V−=Vsig
The output differential current which is the current differential of I+ and I− can be expressed as:I+−I−=Isig
A goal is to make the transconductance or Gm=Isig/Vsig constant with respect to Vsig.
However, in many circuits, transconductance devices 100 exhibit non-linear performance, which can lead to a distorted output differential current signal that is not within an allowed specification.
Therefore, what is needed is a system and method that can allow for a substantially linear transconductance characteristic in a transconductance device. This may be implemented in a device requiring relatively lower power consumption (e.g., DC common mode current or circuit current), no extraneous noise, and operation at very high frequencies (e.g., up to GHz range) compared to conventional transconductance devices.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.